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Hoffman three pitch prop printer friendly version
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Jorgen
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Posted Tuesday, June 10, 2008 @ 04:55 PM  

Hi Guys,
I couldn´t resist beeing the first to post in this section. Anyone else having trouble with pitch shifts with the Hoffman three pitch prop? I think I´m doing the shift according to the recommendations ín the manual (speed 110 km/h, 1500 rpm (if I remember correctly) and then one firm yank of the handle), but most of the time I have to make 3-4 tries before I get cruise pitch, that´s a success rate of about 30 %, not very impressive. Do I just need more practice or is there some adjustment that needs to be made?

Oh, and another thing. I find it´s a good idea to check the mechanism by feathering and un-feathering the prop prior to start-up. That way you ensure you have climb pitch when you take off. The runway gets kind of shorter if you try a take off with cruise pitch set....

Take 5(b) just 4 fun/ Jörgen, SE-UDI, SE-XST

andy1
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Posted Thursday, June 12, 2008 @ 07:11 AM  

So you have one like in Grob G109? If so the HO-62 has different values. To cruise something like 1800-2200 RPM depending on the spring load of the system and to start idle = max 1300 RPM. The system is a pain in the ass if it's not functioning properly. First check that the two ball bearings that contact to the prop flange are OK. Next check that the assy (fork including the bearings) are just in line with the flange. Then check the fork moves far enough and then check the flange and the bearings have correct clearance (can't say any values by heart though...). The locking mechanism itself should be clean and moving correctly, but not too well oiled, because the lock tends to slip. If these adjustments are correct, the pitch should change with one sharp pull. You shouldn't need to pull full back and especially not to keep the handle back. Just a fast pull - not too much force - and release. If it won't work, something is still wrong.

-A-

--------------------
***** Antti Laukkanen, Helsinki, Finland - RF4D OH-371 - RF4D OH-370 - RF5 OH-386 *****

JamesB
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Posted Friday, June 27, 2008 @ 12:27 PM  

I am not sure why you are making a "sharp pull" or "firm yanks." At 2000-2200 rpm, I ease the handle out to feel the bearing engage, then ease it about another inch until I feel the mechanism "shift." 2000 seems a little easier on the mechanism. The bearings on the yoke are well lubed--so it doesn't matter if they ride on the plate a little longer.
Jorgen
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Posted Sunday, July 27, 2008 @ 08:26 AM  

Hi Guys,
thanks for the advices. I checked the mechanism according to Antti´s suggestion and it seems OK. The manual calls for 1900 rpm and 110 km/h when shifting. I tried the "easing out"-method instead of the "firm yank" and I find it easier to shift. Good tip James, especially coming from a yank

Take 5(b) just 4 fun/ Jörgen, SE-UDI, SE-XST

[Edit by Jorgen on Sunday, July 27, 2008 @ 08:37 AM]

jb92563
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Posted Thursday, March 5, 2009 @ 12:53 PM  

I have been practising the shift of the 3 postition HO V-62R prop and the way the Grob manual describes it works easy and gently.

Starting in climb pitch at 1800 rpm or greater pull to cruise pitch.
At Cruise pitch less than 1200 rpm pull to climb pitch.

The trick is the speed at which you shift as there is a centrifical pitch change unit in the hub
that relies on the rpm to allow the proper change so get those rpms right at the shift and it
works easily.

Also I have found the instructions for changing the climb pitch setting if you are not getting the right top end rpms.

It is quite easy to do taking only minutes.

The difference in pitch between climb and cruise is not settable without replacing the adjustment ring parts as I understand it.

[Edit by jb92563 on Monday, August 1, 2011 @ 03:58 PM]

jb92563
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Posted Monday, November 16, 2009 @ 08:06 PM  

There is a Hoffman 3 position prop for sale in the Grob109 yahoo group.
(climb, cruise, feather) V62/160 which is about 62" diameter with 24" pitch climb.

The Guy is in Las Vegas and wants $5k.

It is in great condition and has 400 hrs on it.

They get overhauled every 1000 hrs for certified aircraft or 5 years which ever happen first.

Its a decent price as a new one costs 10k and an overhaul is 2,400 normally to keep it certified.

If anyone is interested I'll post the guys email.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

milnerd
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Posted Monday, August 1, 2011 @ 02:43 PM  

Hi Ray,

On your Grob how many rpm change did you see for one increment change on the pitch?

I have started running up the Walter Mikron in the Vivat in preparation for flying it (very soon I hope). I have been told that 2,350 rpm static will get you to the 2,600 rpm redline at the best climb speed of 54 knots. I am seeing 2,300 rpm static and am wondering whether I should go through the effort to make the pitch one notch finer before I fly it or wait until I see how many rpm I see in the climb.

Best regards

Dave

jb92563
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Posted Monday, August 1, 2011 @ 04:07 PM  

The cruise pitch is about 2300 rpm and the climb pitch gets 2900 rpm.

These are static on the ground rpm's.

So thats ~600 rpm difference.

That translates to a good 400+ fpm climb at about 55 kts at 80F and 1250 ASL.

For 50 rpm I would try it first and see what you get before trying to adjust the pitch lower.

It would take quite a few 1/12ths increments to make a noticeable change. Perhaps 1/12th to make a 5 rpm change.

My redline is ~ 3400 rpm.

[Edit by jb92563 on Monday, August 1, 2011 @ 04:13 PM]

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

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